Instead of replacing dull-looking brass door knobs, use spray paint to give them a fresh new look. Preparing the surface of the door knobs properly ensures that the paint finish adheres well and looks professional. The tools you need to paint brass door knobs are available at home improvement and DIY shops. Select a spray paint and primer developed specifically for painting metal surfaces.
Unscrew the screws that attach the doorknob to the door. You can paint the screws to match or use new screws.
Prepare the surface of the brass by sanding the entire area lightly using a fine-grit sandpaper. Sanding the surface makes the metal rough so that the primer and paint stick well. Wipe away any dust you have created with a clean, dry cloth.
Poke the screws, the neck of the door knob and any other parts into a piece of strong cardboard. Push the screws through so only the screw heads are exposed above the cardboard; push the door knob into the cardboard just enough that the top of the part is steady. The cardboard will keep the pieces upright so that you can easily paint all exposed sides of the parts in one go.
Apply the spray primer to the metal. Follow the manufacturer's directions for use. Shake the can to mix the primer, then remove the lid and spray every surface of the metal in smooth, even lines. Spray at a distance of 30 cm (12 inches) from the parts.
Allow the primed door knob parts to fully dry.
Paint over the primer using spray paint. Follow the manufacturer's directions. Shake the can, remove the lid and spray from 30 cm (12 inches) away. Use long, even strokes to cover all of the door knob parts in an even coat.
Wait until the paint has fully dried.
Remove the parts from the cardboard and reassemble the door knob on the door.
Work in a well-ventilated area when sanding, priming and painting to avoid exposure to dust and fumes. Protect yourself by wearing a mask or respirator.